We used Simple Green Cleaner, from Home Depot for several years and it works just fine.
We have used a product called Simple Green to clean our house for several years now and it works great. It comes in a 22 oz spray bottle that you can use around the house for any cleaning job for about $10. You can buy the larger bottle of concentrate for about $15.
We did not have a pressure washer and used soft brushes with long handles to wash down the walls. The same poles that you use when painting with a roller will fit brushes also. Both can be found at Home Depot.
The had mold and algae in some areas and the cleaner took it right off. I highly recommend it. It worked very well, better than when we used dish washing soap a few years ago.
I think we may use a pressure washer next time just to save time and effort. It costs about $50-$60 to rent a pressure washer.
The name of the product is Simple Green-House and Siding Cleaner. You can find it on Home Depot's web site.